The present invention relates to liquid cleaning of work pieces such as printed circuit boards and wiring boards upon which electric components have been soldered. More specifically the present invention relates to a liquid cleaning apparatus wherein the cleaning occurs substantially within an isolated enclosure which is purged with an inert gas.
Printed circuit boards and the like that have solder deposits thereon after soldering, generally have to be cleaned to remove deposits on the solder from flux resins and the like. Many of the cleaning agents used today to remove these deposits are either flammable or explosive when sprayed in air. Thus liquid cleaning devices are used wherein work pieces are sprayed in an inert environment within an enclosure.
An example of these types of cleaning devices is shown in co-pending application Ser. No. 456,108 filed Dec. 22, 1989. A drying system for a liquid cleaning apparatus is disclosed in co-pending application Ser. No. 574,342 filed Aug. 28, 1990. Furthermore, a liquid cleaning apparatus wherein liquid cleaning agent and water are recycled in a closed loop configuration is disclosed in co-pending application Ser. No. 595,469 filed Oct. 10, 1990. In this latter case the liquid cleaning agents are reused and not dumped or discharged into a sewer or draining system.
When inert gas is provided within an enclosure of a liquid cleaning apparatus, gas and vapors are contained within the enclosed area by providing liquid seals at the entrance and exit to the enclosed area. However, it is generally necessary to withdraw the gases from the enclosed area as they contain vapors. In co-pending application Ser. No. 574,342, the inert gas containing moisture and other vapors passes through a heat exchange condenser. The liquid cleaning agent, water and any other vapors present are condensed prior to the gas either venting or being reused in a dryer tunnel where the work pieces leaving the enclosure are dried. Consequently inert gas must continually be fed into the enclosure to maintain a high percentage of inert gas therein and avoid the possibility of fire or explosion from the volatile liquid cleaning agent.
One such example of liquid cleaning agent used in the liquid cleaning devices is a terpene based solvent. In order to avoid fire or explosion, terpene based solvent is sprayed in a liquid cleaning tank beneath the surface of the liquid cleaning agent to avoid excessive vaporization of the solvent.